Entry of Soil Gas and Radon into Houses

Entry of soil gas and radon into houses has been investigated by a conjunction of experiments conducted at specially designed radon test structures and numerical or analytical modelling. The numerical model solves the steady-state equations for Darcy flow of soil-gas and combined diffusive and advective transport of radon. Model calculations have been compared with results from field experiments conducted at Risø National Laboratory, and it was found that there was good agreement between measured and modelled pressure coupling and radon concentration profiles. However, discrepancies regarding absolute values of soil-gas entry rates and radon concentrations were observed. The numerical model has been used to study the importance of soil and building related factors on radon entry rates into slab-on-grade houses. It was found, that for a house with a 3 mm perimeter crack along the floor-wall joint, the entry was mainly determined by the soil permeability and building related factors such as house depressurization and presence of a capillary breaking layer of gravel below the slab. For a house with a bare soil floor, the diffusivity of the soil was found to be of principal importance for the entry rate even for moderate permeabilities. Finally, an analytical model has been developed for the purpose of studying soil-gas entry rates into houses in response to non-static driving forces. The model is based on the analogy between a "buried drain' and a basement house with a perimeter crack. The modelling results have been compared with experiments conducted at a test structure at the Lawrence Berkeley Laboratory. The structure was depressurized sinusoidally in time and the frequency dependent pressure couplings were measured. There was fairly good agreement between theoretical and experimental results given the simplifying assumptions underlying the model.